Optical Nerve Sheath Changes During Head Down Laparoscopy

"In cases: ultrasound measurement of the diameter of the optical nerve sheath at (T1) baseline before the induction of general anesthesia (5 min after the beginning of mechanical ventilation in supine position); (T2) after 10 min from 25 degrees head down positioning and with pneumoperitoneum insufflation; (T3) after 60 min from T2, in head down position; (T4) after 10 min from tracheal tube removal, in supine position.~In healthy controls: ultrasound measurement of the diameter of the optical nerve sheath at (T1) baseline in supine position; (T2) after 10 min from 25 degrees head down positioning; (T3) after 60 min from T2, in a head down position; (T4) after 10 min from positioning supine"